A ubiquitous network technology has captured the world's attention. The ubiquitous network technology allows a user to naturally access various networks regardless of time and location.
Such a ubiquitous network technology comprises a radio frequency identification (RFID) technology and a ubiquitous sensor network (USN) technology. Among them, the RFID technology for commercial transaction is representatively employed.
The ubiquitous sensor network (USN) technology is referred to as a network technology of constructing a network such that plural pieces of information collected by various sensors are obtained in wireless. According to the USN technology, a plurality of sensor network nodes are installed in a region where the access of a person is difficult, thereby allowing the person to monitor the region.
An RFID system for commercial transaction comprises an RFID tag attached to goods and equipped with detailed information about the goods and an RFID reader for reading the detailed information embedded in the RFID tag through RF communication. The RFID tag attached to the goods transmits the information to the RFID reader through RF communication while passing through an area where the RFID reader is positioned. Accordingly, there is provided an infrastructure capable of effectively processing supply chain management (SCM) including the distribution, the assembly, the price change, and the marketing of goods.
A related RFID system comprises a reader and a tag, and the reader periodically transmits an information requesting signal to establish an RFID communication channel with tags entering a radio region of an antenna, and collects information about the tags.
In this case, since the reader collects information about an unspecified number of tags, the reader always transmits the information requesting signal under high power. Accordingly, such a communication scheme may degrade the efficiency of hardware resources and cause serious power waste.
For example, since the reader has to periodically transmit the information requesting signal regardless of the entrance state of a tag into a communication region, and a main operation circuit operates in a full mode and maintains an idle state, the load of a circuit unnecessarily increases and a great amount of power is dissipated.
In order to overcome such an inefficient communication scheme, a scheme to employ an additional detector has been suggested. For example, a plurality of detectors, such as an optical (infrared) sensor and a vibration (ultrasonic) sensor, monitor a communication region of a reader, and transmit an operational signal to the reader if an object is detected.
The reader transmits the information requesting signal and activates circuits and operational resources used to make RFID communication with the tag if the operational signal is received in the reader through a network including a serial cable.
However, a plurality of detectors are added, so that installation costs increase, a network structure becomes complex, and software and hardware resources are additionally required in order to process signals delivered from the detectors.